Air seeders are commonly towed by tractors to apply seed or fertilizer, or both simultaneously, to a field. It is generally advantageous to tow an air seeder in combination with a tilling implement, one behind the other, to place the seed and fertilizer under the surface of the soil. An air seeder has as its central component a wheeled seed cart which comprises one or more frame-mounted seed tanks for holding product, generally seed or fertilizer or both. Air seeders also generally comprise a metering system for dispensing product from the tanks and a pneumatic distribution system for delivering the product from tank to soil.
It is known to provide an air seeder with volumetric meters which measure a fixed volume of seed per unit of linear distance. These volumetric meters typically comprise either augers or fluted cylinders (meter rollers) which rotate through a product reservoir to measure granular product, as illustrated in U.S. Pat Nos. 3,489,321 and 3,763,797. As the meter rollers continue their rotation, metered product is fed into a pneumatic distribution system. The pneumatic distribution system of an air seeder generally utilizes a centrifugal fan to provide at least one airstream which flows through the pneumatic distribution system to seed boots where product is deposited in the soil. Product is first introduced to the air stream by the metering system at a primary distribution manifold located below the metering system. Product is carried by the air stream through distribution lines to a series of secondary distribution manifolds ("headers"), which in turn distribute product through distribution lines to seed boots mounted behind ground openers on the tilling implement so that the product may be evenly delivered to the span of ground (the "tillage") acted upon by the tilling implement.
Secondary distribution headers ideally have product requirements proportional to the number of ground openers they service. Since the number of ground openers is often not evenly divisible by the number of headers, one header may service a different number of seed boots than another header. Because a header has one outlet port for each seed boot it services, headers often have varying numbers of outlet ports, Therefore, in order to evenly distribute product across the width of the tilling implement, product seen by a secondary distribution header servicing 10 seed boots, for example, should be less than (5/6) the amount of product seen by a secondary distribution header servicing 12 seed boots. The meter roller upstream in the pneumatic distribution system from the secondary distribution header servicing fewer seed boots should therefore supply a lesser volume of product.
A known method for reducing the product metering rate involves removing a roller which services a port in the primary distribution manifold. Since the primary distribution manifold has one outlet port for each downstream secondary distribution header, the header, as well as all of the seed boots serviced by that header, receive no product.
An alternative method which is old in the art utilizes meter rollers of varying widths, with spacers to their sides. This method is difficult to customize, and placing spacers to the sides of the meter roller prevents optimal flow of product through the air stream.
Accordingly, conventional air seeders are unable to properly ration product to secondary distribution headers, and therefore have problems maintaining an acceptable distribution of seed or fertilizer across the width of the tillage.
Therefore, it is desirable to devise a metering system which can accommodate varying product requirements seen by individual meter rollers which are driven by a common shaft.
It is also desirable to devise a metering system which, in conjunction with a pneumatic distribution system and a tilling implement, provides substantially uniform product distribution across the tillage.